Effective heating chamber design to simulate acute heatwaves and night-time warming for ecological communities under natural field conditions

Abstract

Heatwaves are increasing in intensity, duration and frequency. The impacts of such events can be extensive for natural ecosystems, but studying heatwaves in field conditions (in situ) remains challenging. Chambers that passively increase air temperatures have been used widely for studying climate warming in field experiments, but they cannot simulate warming at night and rarely achieve more than +3°C above ambient air temperature. Simulating heatwaves requires active heating. As a result, most studies of heatwaves have been applied ex situ to potted plants or mesocosms, which can yield results that do not reflect outcomes in natural systems. We designed and built equipment for simulating an extreme heat event under field conditions that combines passive warming in semi-enclosed chambers and active convective heating, using portable diesel heaters to supply warm air to 1.5 m diameter cylindrical chambers. The active heating systems can be programmed with target temperature profiles to heat day and night. Through two case studies in high elevation ecosystems in Australia, we demonstrated the capacity for an actively heated chamber to increase air temperature by up to +14°C above ambient during the day and +17°C at night, then identify optimal operating conditions and limitations during challenging field conditions. Our active heating chamber design can be applied to simulate an array of extreme heat scenarios on ecological communities, including night-time warming, daytime extremes, varying heat intensity, duration, event frequency, recovery period lengths and combinations thereof. We hope that researchers will be inspired to make use of this active heating chamber system to study the impacts of heat in the field.